The invention relates generally to apparatus and methods for dispensing fluids onto a surface using a felt applicator. More particularly, the invention relates to a flow through felt dispenser that utilizes one or more dispensing heads and additional features to provide a more uniform and consistent bead or film to the surface.
Many industries utilize dispensing systems to apply liquid material to a surface. In the motor vehicle industry, for example, liquid primers are applied to a perimeter region of a windshield as part of the process for installing a windshield in a vehicle body. These primers may be of various types and are preparatory to applying a urethane bead to the windshield that bonds the windshield to the frame. In a typical process, the windshield manufacturer applies a roughened black ceramic frit to a marginal or perimeter region of the windshield on the side of the glass that is bonded to the frame. Before the urethane bonding material can be applied to the frit, a first type of primer must be applied to the surface of the frit with a rubbing action. Often this first type primer is clear in color and is a surface activator that quickly evaporates and prepares the frit surface for application of a second type primer. In order to be effective, however, the clear primer cannot be simply applied but must be applied with a rubbing action as well.
After the clear primer is applied, a second type primer is applied to the frit, again with a rubbing action. Typically the second primer is black in color. The black primer improves adhesion of the urethane to the frit, but more importantly functions to block ultraviolet radiation that would otherwise cause degradation of the urethane. The black primer tends to have a higher viscosity than the clear primer, with the latter having a viscosity about that of water. A typical black primer may have a viscosity, for example, of about 40-100 centipoise.
The primers may be applied to the windshield by manual operations, but more commonly they are applied by dispensing the primer onto the frit using a liquid dispensing gun, and then applying a rubbing action by robotically moving a piece of felt across the frit by relative movement between the windshield and the gun. In a known process commonly referred to as xe2x80x9cdrip and dragxe2x80x9d, the primer is applied onto the frit just ahead of the felt. The primer may be intermittently applied rather than continuously. When the type of the primer is changed, the felt must be changed or an opposite surface of the same felt piece used.
One such system utilizing a drip and drag process is disclosed in U.S. Pat. Nos. 5,277,927 and 5,370,905 which are owned by the assignee of the present invention, the entire disclosures of which are fully incorporated herein by reference. These patents provide a more detailed description of such apparatus and the various technical issues involved with applying these primers to a windshield.
Although the above referenced systems are a significant advance in the art, they as well as other known systems have limitations. For example, the known systems require manual changeover of the felt piece either for each type primer change or after each windshield is completed. This results in a substantial consumption of the felt material. The process of applying the primers to the frit tends to cause splashing of the primer onto surfaces that should not have primer. Still further, most vehicle windshields are not flat panes of glass but rather are curved, some more than others, particularly near the marginal area or perimeter. This can cause a loss of or diminished contact between the felt applicator and the frit, especially as the robotic arm passes around corners. Another drawback to a drip and drag process is an uneven bead profile, particularly of the more viscous black primer. The felt tends to push the primer ahead of it, thereby diverting primer to either side resulting in a xe2x80x9crailroad trackxe2x80x9d profile in which the edges of the bead are thicker than the center region of the bead. Additionally, since the primers are applied by pulsing a dispensing gun on and off, it is difficult to control the amount of liquid material applied to the frit.
The need exists therefore to provide a process and apparatus for applying liquid material to a surface with a rubbing contact or action that overcomes or diminishes the aforementioned limitations of known systems.
The invention contemplates in one embodiment a liquid dispensing system that utilizes a flow through application process. In accordance with one aspect of the invention, the dispensing system uses two dispensing heads. Each head may dispense a liquid material that is of a different type (for example, possibly a different color or viscosity) than the other dispensing head. Each dispensing head may be presented to a surface, such as a windshield, and placed in contact with the surface, with the other dispensing head out of contact with the surface. The dispensing heads may be disposed side by side on a frame such that by applying a slight tilt or rotation of the frame only one dispensing head at a time contacts the surface.
In accordance with another aspect of the invention, each dispensing head utilizes a flow through process for applying liquid material to the surface. In one embodiment, a flow through process is realized by the use of a porous material, such as a felt web, that is held in position on each dispensing head. Each dispensing head includes a valve that controls flow of liquid material to the porous material. A rub block supports a portion of the porous material proximate to an outlet orifice of the valve. In accordance with another aspect of the invention, the rub block is configured to permit the block to be compliant or adjustable about at least one axis to improve contact between the porous material and an irregular surface. In one embodiment, the valve includes a ball nozzle and the rub block is installed on the ball so as to be able to pivot or swivel as the dispensing head traverses the surface. In accordance with another aspect of the invention, the rub block may further include a recess, pocket or galley between the valve orifice and the porous material to improve the bead profile of the liquid material applied to the surface.
In accordance with another aspect of the invention, a flow through liquid dispensing system is provided with an improved bead profile. The improved bead profile is achieved by use of the rub block galley design, as well as use of a pressure regulator, nozzle orifice size and a flow meter as a system or arrangement for controlling the amount of liquid material dispensed through the nozzle. Accurate volume and pressure control of the liquid material can thus be achieved during a dispensing operation rather than relying on triggering properties of the dispensing valve. The improved bead profile is more consistently produced and includes a greater volume of material near the center of the bead and less volume along the edges of the bead.
Various aspects of the present invention may also be used in a single dispensing head configuration.
These and other aspects and advantages of the present invention will be readily appreciated and understood from the following detailed description of the invention in view of the accompanying drawings.